Both Careers have started the same, both Pujols and Mike Trout became the best players in Baseball in a very short time.
An argument for Pujols would be him becoming a once in a generation type talent, especially with the bat right from the get go. This was one of the few handful of players that could touch what Barry Bonds did with the bat. Not only was he a generational hitter but he quickly became the best, or one of the best fielding first baseman in baseball. The knock on him of course is once injuries and one can assume age became a big factor his production with the bat fell into a ditch. However this can not take away much what he accomplished in St Louis.
The Argument for Trout is obviously that he became the best overall outfielder in 2 seasons, and many can argue 1. While I doubt his bat will be as potent as Pujol's was there's no denying he plays a much more important position in regards to defense and plays it as one of the best outfielders, if not the best defensive outfielder in the game. Even if his bat won't equal what Pujols accomplished there's no denying he's a top hitter in baseball, and arguably the best offensive outfielder in baseball especially when you consider his speed. The only real knock on him is his career has just gotten started and he hasn't accomplished as much as Pujols did in
St Louis, this of course doesn't mean he can't. Anything can happen as you can't predict injuries or how if he gets better or worse, and even if he does regress in season 3, he'd still have a very good chance at being the best player in baseball.